


Fireworks

by TheSinnabun



Category: Undertale (Video Game)
Genre: Exhibitionism, M/M, Multi, Tentacles, Voyeurism, i am a filthy filthy sinner
Language: English
Status: Completed
Published: 2015-12-19
Updated: 2015-12-19
Packaged: 2018-05-07 14:57:51
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,458
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5460587
Author URL: https://archiveofourown.org/users/TheSinnabun/pseuds/TheSinnabun
Summary: <blockquote class="userstuff">
              <p>It had to be a team effort. Grillby was able to hold himself well against one, but the two of them? He wouldn't stand a chance.</p>
            </blockquote>





	Fireworks

**Author's Note:**

> This is all under the notion that Gaster and Sans are not related, I don't do incest.
> 
> Tumblr mirror here > http://thesinnabun.tumblr.com/post/135498984440/and-tonight-on-im-a-filthy-sinner-title

It had to be a team effort. Grillby was able to hold himself well against one, but the two of them? He wouldn't stand a chance.

Sans and Gaster have worked together for years. And even after the incident, Gaster's methods haven't changed a bit. It was easy for the two of them to fall back into a well-oiled machine, two cogs working perfectly in sync. They walk into the restaurant as Grillby's closing down and sit at the bar, ordering their usual.

Gaster would even butter the entrepreneur up by helping him clean up after he locks up. Sans of course would just sit back and watch, luring Grillby into a false sense of security with back and forth banter with Gaster. Gaster might be able to dish out puns, but he certainly couldn't take them. Seeing the not-so-solid skeleton flare up in his cringing was always something Grillby liked.

Once the money's counted Grillby goes to Gaster to give him a hug. "...Thank you for helping me finish early tonight." The elemental would finally speak. Gaster's smile could barely hide the mischief he felt; the fact he spoke more than three words was a good sign. Sans stared at the back of their prey's head, half lidded and knowing.

The kiss would start innocently enough. "IT WAS A PLEASURE TO HELP." But Gaster's attached hands would start to roam, earning a flicker of the flame head. In Grillby's moment of hesitance Gaster would push the boundaries, as well as push Grillby against the side of the counter. Grillby would try to resist, being a much more well-mannered man than he, but Sans leering at him made him blue in embarrassment.

"you have to admit, grilbz," Sans would start, and Gaster's focus on exploring Grillby's body would intensify. It would steel him from what would come next. "gaster is pretty _hand_ y to have around."

Grillby's concentration would break as he turned to Sans. But whatever he was going to say was lost when another pair of hands, floating and powerful, would join Gaster's original pair. These ones were far less intimate, groping at everything warm they touched. Namely, every part of Grillby they can reach. The rest would be too easy now.

"fuck, you two..." Sans would let out, eyes and a roaming hand betraying his lust, as Gaster becomes more aggressive in his teasing. Sans would have it pretty easy. He would get dinner _and_  a show. It worked out for him, since he didn't have to do much more than he liked doing. Not to mention, it was rather fun to watch. He would have to guess that he was some kind of freak.

Then again, that would mean Grillby had to be a little bit of a freak too, since he would like being watched.

A moan. A moan would escape Grillby's fiery throat as an inky appendage slipped under his belt. A mouth would form and provide the perfect opening for an equally inhuman tongue. The "kiss" would become passionate, and as the other tendril would easily wriggle it's way along the curve of his groin Grillby's lust would get the better of him. He would warmly welcome the intruding tongue, giving it the tiniest suck.

It would be enough for Gaster to go even further, to become even more domineering. Grillby would be turned around and his chest would be pressed against the countertop, but not before Gaster remove and toss Grillby's shirt.

Sans would enjoy the show a little too much. Watching Gaster press his hips against Grillby's, hearing Grillby become more vocal with his rising pleasure and need, of course it would be too hard to just sit there and do nothing. So he would sit there and enjoy himself. He would shudder as his hand did more work than he would admit, left eye aglow and trained on the two before him.

"you two are going to give my arm a real work out, you know?"

Gaster would ignore him, having his attention divided between his multitasking. Sure it came natural for him to make use of his new tricks from the void, but being able to even experience the touches and the taste of Grillby took a special, scientific concentration.

Grillby would be putty underneath him. He couldn't see Gaster behind him, but he could still see Sans, grinning devilishly as he enjoyed the show. Grillby would be helpless; unable to speak because of the tentacle-like tongue stuffing his mouth and unable to move because of the floating hands holding his wrists behind his back. A third pair would show themselves, one pressing his head down and the other tugging his pants down impatiently.

Unless Grillby closed his eyes, he wouldn't be able to stop watching Sans get more worked up as they made eye contact. But Grillby wouldn't. He couldn't. He would know what was going to happen. He was going to be taken right there on the counter, in his pub, all while his best customer watched. It was going to be embarrassing. It was going to be downright humiliating.

It was going to be _absolutely thrilling._

Gaster would whisper lewd things as he lowered his head behind Grillby's. At least, they could be considered whispers, considering his lack of volume control. Or maybe it would be intentional for Sans to hear every word. Sans would certainly chip in with the right words to make Grillby squirm.

Despite being literally fire, Grillby would always take a surprising amount of time to get warmed up. It would be a slow burn, being teased mercilessly by the two of them in various ways, before Grillby was a roaring fire of need and desire. "...P..please." He'd manage to get out around Gaster's tongue.

"what was that, grilbz?" Sans would goad, still lazily stroking himself.

"Please!" Grillby would always swallow his pride, steam escaping his mouth as Gaster's tongue pulled out, no longer drooling. "I can't take this anymore!"

Gaster wouldn't be able to resist any longer. The fun of the hunt would be over by now, and knowing he won he would take his prey. His hands grabbing Grillby's exposed hips, Gaster would finally push himself in, earning Sans groans of relief and pleasure from the two of them. The slow build up would pay off, and nothing would be able to quench the flame.

Sans's stroking would match Gaster's reckless pace, his free hand balling up and pressing against the counter top. His breath would hitch, though would not be nearly as ragged as poor Grillby's.

No, Sans's panting was nothing compared to Grillby's guttural moans of pleasure, as he was fucked with abandon. Gaster's noises would be filled with purrs and growling, barely able to get his words out. Gaster was certainly the most experienced and talented of the three as he kept up the dirty talking. Gaster would do most of the work, but that wouldn't be anything new to him and Sans.

Sans would be the first to drop out. A final shudder, a gasp would push out as he came. He normally could last longer, but he wouldn't dream of missing what was approaching. Panting and regaining a steady breathing pattern, he would glance at Gaster. Gaster would be starting to get impatient, doubling his efforts as every part of him groped and pinched and stroked Grillby's erogenous zones. Sans would decide to give one last bit of effort and look back at Grillby.

"you starting to get close yet? are you really enjoying this, being watched?" Sans would certainly have a way with words, hitting all the right buttons. "yeah, you really are kind of a freak, grilbz. you don't gotta hold back in front of me, you know."

Grillby and Gaster would tie. Gaster would give one last thrust before he spilled over, and the cold sensation would be enough to push Grillby over the edge. Grillby was surprisingly quite when he climaxed. The real treat was watching him, not hearing him.

Grillby was a wonder to watch when he finally lost it. This would be no different here. His entire body would flush a bright wine color, sparks flying and fire coming out of his now-wide-open mouth. It was a beautiful fireworks show, just for the two scientists.

When Grillby would finally come down from his high, he would fall from his arched position, trembling slightly and breathing heavily. Gaster would stay still, his extra appendages fading away as he wrapped his arms around his oldest lover and nuzzling against his back. Sans would watch the two affectionately, chin in clean hand.

"fuck, you two..." Sans would repeat, affection softening his tone. "you two are really fun to watch."


End file.
